The Islamic Revolutionary Guard Corps, which accused Saudi Arabia of involvement in the attacks, vowed to avenge the bloodshed.

Senior Iranian officials had also put the blame on Riyadh after the Tehran attacks, saying Saudi Arabia was “promoting terrorist groups” in Iran.

The Islamic republic of Iran is a key ally of the Syrian regime of President Bashar al-Assad, alongside Russia and the Iran-backed Hezbollah movement of Lebanon.

Iran has sent to Syria military advisers as well as thousands of “volunteer” fighters recruited among its own nationals as well as the Shiite communities in neighbouring Afghanistan and Pakistan since Syria’s conflict broke out in March 2011.

According to a report published in March, some 2,100 combatants sent by Iran have died in Syria and Iraq.